Maintaining the desired quality of fluids by passing or circulating the fluid through a filtering medium is important for various applications, for example those dealing with filtration of drinking water. Filtration is generally recognized as an effective means of removing solid particles and/or dissolved matter and/or biological agents routinely present in the water. The choice of which filtration methodology to use from the great variety of available technologies depends on characteristics and/or degree of contamination of water to be filtered and/or manufacturing costs and/or operational costs of the filtration methodology.
Various techniques for filtering liquids, particularly such for filtering water to obtain potable water, have been developed. These techniques typically utilize a filtering medium through which water passes. In some cases, a filtration process involves multiple stages, with each stage designed for a specific type or group of contaminants.
Examples of the filters, filtration techniques and filtering media are described in U.S. Pat. No. 7,311,829; WO 08/044230; WO 08/129551; and WO 08/026208 all assigned to the assignee of the present application.
Filtering media used in fluid filters have limited useful lifetimes after which the filtering media become saturated with filtered out impurities or contaminants and cease to be effective in their removal from the fluid. Means for indicating when a filter reaches the end of its useful life are important for many applications. Filter devices utilizing means for indicating to a user the status of the filter device, thus allowing the user to identify that the filter has become ineffective, have been developed. Such devices are described for example in U.S. Pat. Nos. 4,681,677; 5,997,734 and 6,491,811; as well the above-indicated International publication WO 08/044230.